Supercooling means that a molten object or a solid cooled below a phase transition temperature in a balanced state is not changed. Each material has stable states in each temperature. If the temperature is slowly varied, elements of the material maintain the stable states in each temperature and accompany the variations of the temperature. However, if the temperature is sharply varied, the elements cannot be changed into the stable states in each temperature. Therefore, the elements of the material maintain the stable state of the start temperature, or some of the elements fail to be changed into the state of the final temperature.
For example, when water is slowly cooled, it is not frozen temporarily at a temperature below 0° C. However, when water is supercooled, it has a kind of quasi-stable state. As this unstable balanced state is broken even by a slight stimulus, water tends to be changed into a mare stable state. That is, if a small piece of material is put into the supercooled liquid, or if the liquid is suddenly shaken, the liquid is directly frozen so that the temperature of the liquid can reach the freezing point. Accordingly, the liquid maintains a stable balanced state at the temperature.
In general, an electrostatic atmosphere is made in a refrigerator, and meats and fishes are thawed in the refrigerator at a minus temperature. In addition, fruits are kept fresh in the refrigerator.
This technology uses supercooling. Supercooling means that a molten object or a solid cooled below a phase transition temperature in a balanced state is not changed.
This technology is mentioned in Korea Laid-Open Patent Official Gazette 2000-0011081 disclosing an electrostatic field processing method, an electrostatic field processing apparatus, and electrodes therefor.
FIG. 1 is a view illustrating an embodiment of a conventional apparatus for thawing and freshness keeping. A cooling box 1 includes an insulation 2 and an outer wall 5. A temperature control device (not shown) is installed in the cooling box 1. A metal shelf 7 installed in the cooling box 1 has a two layer structure. Vegetables, meats or marine products are minted on each layer for thawing, freshness keeping or ripening. The metal shelf 7 is isolated from the bottom of the cooling box 1 by insulators 9. A high voltage generating device 3 can generate 0 to 5000V of DC and AC voltages. The inner surface of the insulation 2 is covered with an insulating plate 2a such as vinyl chloride. A high voltage cable 4 for outputting the voltage of the high voltage generating device 3 accesses the metal shelf 7 through the cuter wall 5 and the insulation 2.
When the user opens a door 6 installed on the front surface of the cooling box 1, a safety switch 13 (refer to FIG. 2) is turned off to block the output of the high voltage generating device 3.
FIG. 2 is a circuit view illustrating the circuit configuration of the high voltage generating device 3. 100V of AC is supplied to a primary side of a voltage adjusting transformer 15. Reference numeral 11 denotes a power lamp and 19 denotes an operation state lamp. When the door 6 is closed and the safety switch 13 is on, a relay 14 is operated. The operation of the relay 14 is displayed by a relay operation lamp 12. Relay contact points 14a, 14b, and 14c are closed by the operation of the relay 14, and 100V of AC is applied to the primary side of the voltage adjusting transformer 15.
The applied voltage is adjusted by an adjusting knob 15a at a secondary side of the voltage adjusting transformer 15. The adjusted voltage is displayed on a voltmeter. The adjusting knob 15a is connected to a primary side of a boosting transformer 17 at the secondary side of the voltage adjusting transformer 15. The boosting transformer 17 boosts a voltage at a rate of 1:50. For example, when 60V of voltage is applied, it is boosted to 3000V.
One end O1 of the secondary side output of the boosting transformer 17 is connected to the metal shelf 7 isolated from the cooling box 1 through the high voltage cable 4, and the other end O2 of the output is earthed. Since the cuter wall 5 is earthed, if the user contacts the cuter wall 5 of the cooling box 1, he/she does not receive an electric shock. In FIG. 1, the metal shelf 7 exposed in the cooling box 1 must be maintained in an insulated state. It is thus necessary to separate the metal shelf 7 from the walls of the cooling box 1 (the air performs insulation). If the contents 8 mounted on the metal shelf 7 contact the walls of the cooling box 1, the current flows to the grand through the walls of the cooling box 1. Drop of the applied voltage is prevented by adhering the insulating plate 2a to the inner walls. When the metal shelf 7 is not exposed but covered with vinyl chloride, an electric field atmosphere is made in the whole cooling box 1.
In the conventional art, since an electric field or a magnetic field is applied to the contents to be cooled and stored so that the contents can enter a supercooled state, a complicated apparatus for generating an electric field or a magnetic field should be provided in order to house the contents in the supercooled state, and a high power consumption for the generation of an electric field or a magnetic field is required. In addition, such an apparatus for generating an electric field or magnetic field has to additionally have an apparatus (for example, an electric field or magnetic field shielding structure, interrupting device, etc.) for the user safety upon generation and interception of an electric field or magnetic field the to high power.